1. Field of the Invention
The present invention relates to a sheet-shaped adhesive useful as a transparent adhesive layer used in the preparation of a film-reinforced glass or a laminated glass which has excellent impact resistance and penetration resistance (resistance to passing through) and is effective in prevention of crimes, and which is used in an automobile, a railway vehicle, a building and a showcase, and laminates such as a film-reinforced glass and a laminated glass prepared by using the adhesive.
2. Description of the Related Art
As a glass used in automobile, especially windshield, a laminated glass having a structure that two glass plates are bonded through a transparent adhesive layer (intermediate layer) is generally employed. The transparent adhesive layer is, for example, composed of PVB (polyvinyl butyral) or EVA (ethylene-vinyl acetate), and the use of the transparent adhesive layer enhances penetration resistance of the laminated glass. If external impact is given to the laminated glass, the transparent adhesive layer prevents the glass broken by the impact from scattering because the layer adheres to pieces of the broken glass. Even if the laminated glass for automobile is destroyed for the purpose of robbery or invasion, the window of the laminated glass cannot be opened. Hence, the laminated glass is useful as glass for prevention of crimes. The laminated glass is, for example, described in JP2002-187746A.
In contrast, side windows (side glasses) such as door glass and a glass inserted in window in automobile are scarcely destroyed due to traffic accident, and therefore the glasses do not need such excellent penetration resistance as the above-mentioned laminated glass has. As a result, for the door glass, one glass plate consisting of slightly reinforcing glass has been employed. However, in case only such a glass plate is used in the door glass, the use brings about the following disadvantages:
(1) the glass is poor in impact resistance and penetration resistance (passing through resistance) compared with the laminated glass;
(2) if the glass is destroyed for the purpose of robbery or invasion, it turns into many pieces of the glass to permit window to open.
Therefore, it is also now under investigation to use a glass having characteristics of the laminated glass for the side window of an automobile (e.g. a door glass or inserted glass).
As the laminated glass, especially the door glass of automobile, JP2002-046217A and JP2002-068785A describe a film-reinforced glass in which a plastic film is superposed on a glass plate through a transparent adhesive layer.
Hence, the transparent adhesive layer (i.e., sheet-shaped adhesive) having function that bonds two glass plates to each other or a glass plate (for film-reinforced glass) to a plastic film is required to have excellent adhesion and penetration resistance mentioned above.
It often happens that environmental pollution of chemical materials become problems recently. Hence it is also required not to use the chemical materials bringing about environmental pollution in the transparent adhesive layer. For example, JP2002-046217A and JP2002-068785A use 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane as crosslinker (organic peroxide) for cross-linking ethylene-vinyl acetate copolymer in Example. The crosslinker cross-links the ethylene-vinyl acetate copolymer for relatively short time to bring about a sheet having excellent adhesion properties and penetration resistance.